Added logic for tags and audio engine.

Harmonia.Core/Playlists/IPlaylistManager.cs

@@ -0,0 +1,13 @@
+namespace Harmonia.Core.Playlists;
+
+public interface IPlaylistManager
+{
+    Playlist? CurrentPlaylist { get; set; }
+
+    void AddPlaylist();
+    void RemovePlaylist(Playlist playlist);
+
+    event EventHandler? CurrentPlaylistChanged;
+    event EventHandler<PlaylistAddedEventArgs> PlaylistAdded;
+    event EventHandler<PlaylistRemovedEventArgs> PlaylistRemoved;
+}